Pottery butter keepers are available in a variety of styles from round to cylindrical to square. They are typically made up of a small, bell-shaped top that is placed open-side down inside a base filled with water.
Though butter keepers typically have the same two-piece design, the appearance can range from a classic blue and white painted ceramic to sleek, angular and modern white cubes. Most butter keepers are made from pottery, but they may also be marble, glass, stainless steel or other insulating materials that keep butter fresh.
Butter keepers are a popular way to store butter at room temperature, which makes it easy to spread on bread or use for cooking. Rather than relying on refrigeration to keep butter fresh, butter keepers rely on a little water in the base. The water creates a vacuum seal when the bell-shaped top is filled with butter and overturned onto the base. This vacuum seal helps keep butter fresh, and the insulating walls of the butter keeper help to keep the butter cool while it sits on the kitchen counter. If stored in a butter keeper, butter can be kept on the kitchen counter for up to 30 days without spoiling.